1. Field of the Invention
The present invention is directed to a closed system such as a transcutaneous energy transfer (TET) system and, in particular, to a dual power supply switching system for a TET system wherein powering of an implantable medical device and its associated components is switched, during communication from the external device to the implant, between an internal power source of the implantable medical device and an external RF power source produced by the external device.
2. Description of Related Art
In a variety of scientific, industrial, and medically related applications, it may be desirable to transfer energy or power (energy per unit time) across some type of boundary. For example, one or more devices that require power (e.g., electrical, mechanical, optical, and acoustic devices) may be located within the confines of a closed system, or “body,” in which it may be difficult and/or undesirable to also include a substantial and/or long term source of power. The closed system or body may be delimited by various types of physical boundaries, and the system internal to the boundary may be living or inanimate, may perform a variety of functions, and may have a variety of operational and physical requirements and/or constraints. In some cases, such requirements and constraints may make the implementation of a substantial and/or long term “internal” power source for internally located devices problematic.
In some closed systems, repeated entry into the system may be undesirable for a variety of reasons. In other closed systems, significant internal power requirements and a limited internal space may prohibit the implementation of a suitably sized internal power source. In yet other systems, contamination and/or security issues may pose particular challenges in implementing an internal power source. For any combination of the foregoing and other reasons, a power source external to the system and some feasible means of transferring power from the external source to one or more internal devices may be preferable in some applications.
One common example of a closed system is the human body. In some medically related and scientific applications, a variety of prosthetic and other medical devices that require power may be surgically implanted within various portions of the body. Some examples of such devices include, but are not limited to, drug infusion pumps, pacemakers, defibrillators, cochlear implants, sensors and stimulators. With respect to the human body, issues such as repeated reentry or surgery, internal space limitations, and contamination (e.g., infection) are factors to consider when selecting a suitable internal power source for some of these implantable medical devices.
Accordingly, in some medical implant applications, “transcutaneous energy transfer” (TET) devices are employed to transfer energy from outside the body to inside the body, to provide power to one or more implanted prostheses or devices from an external power source. One example of a conventional TET device is a transformer that includes a primary winding (or coil) external to the body and a secondary winding internal to the body. Both the primary and secondary windings generally are placed proximate to respective outer and inner layers of a patient's skin; hence, the term “transcutaneous” commonly refers to energy transfer “through the skin.” Energy is transferred from the primary winding to the secondary winding in the form of an RF field.
In a system employing an implantable medical device and external control unit each of the implantable medical device and external control unit preferably has its own power source, e.g., a battery, for powering its associated circuitry and its associated components. The implantable medical device battery, regardless of whether primary/non-rechargeable or secondary/rechargeable, has a limited lifespan and a predetermined amount of energy or power before having to be replaced or recharged.
It is therefore desirable to develop and an improved TET system having circuitry for optimally switching from an internal power source to an external RF power source so as to reduce the energy consumed from the internal power source associated with the implant.